Скачать или смотреть Understanding GraphQL Unions: Why createUnionType Cannot Be Used as InputType

Discover why GraphQL unions like `createUnionType` can't be used as InputType and what alternatives you have in type-graphql.
---
This video is based on the question https://stackoverflow.com/q/67784481/ asked by the user 'David Faizulaev' ( https://stackoverflow.com/u/1850978/ ) and on the answer https://stackoverflow.com/a/68206894/ provided by the user 'Michał Lytek' ( https://stackoverflow.com/u/5472617/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Type graphql - set createUnionType as InputType

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding GraphQL Unions: Why createUnionType Cannot Be Used as InputType

In the world of GraphQL, unions are a powerful feature that allows you to define a type that can return one of several different object types. However, when you're using the type-graphql framework to set up these unions, you may encounter situations that lead to confusion—especially when it concerns using union types as input types. One common scenario involves an error message stating: "Cannot determine GraphQL input type for userActions."

What's the Issue?

You may have configured a union type using the createUnionType function in type-graphql like below:

[[See Video to Reveal this Text or Code Snippet]]

Even though this setup looks perfectly valid for defining a union in your GraphQL schema, you might run into the problem that GraphQL does not allow union types to be used as input types.

So, why are you encountering that error?

The Limitation of GraphQL Unions

GraphQL, by its specification, restricts unions to being used only for output types—not input types. The union types are designed to enable a field to return different types of objects, providing flexibility in your responses. However, when it comes to input, GraphQL maintains a strict type system for predictability and to facilitate validation.

Key Points to Remember:

Unions are for Output Only: They cannot be utilized as input types.

Structured Input: GraphQL encourages a more structured approach to input types to ensure clear and understandable API interactions.

Alternative Solutions

Now that we know that unions can't be used as input types, what can we do instead? Here are some alternative approaches:

1. Use Interfaces

Instead of using unions, you could consider using GraphQL interfaces. Interfaces allow different object types to share common fields. You can create a single input type that encompasses the shared fields and implement these shared fields in each of your object types.

Example:

[[See Video to Reveal this Text or Code Snippet]]

2. Define Separate Input Types

Create distinct input types for each action. This approach can simplify your client-side code, as each operation can identify exactly which fields are required for each action type.

Example:

[[See Video to Reveal this Text or Code Snippet]]

3. Use Union-like Structures with Specific Input Fields

You might also consider designing a custom input field structure that includes a field to indicate the action type and another set of fields specific to the action.

Example:

[[See Video to Reveal this Text or Code Snippet]]

This last structure allows the client to specify which input data is relevant while still adhering to GraphQL's strict type system.

Conclusion

In summary, GraphQL unions are strictly designed for output types and cannot serve as input types. When dealing with mutations where varying input structures are needed, consider alternatives such as interfaces, distinct input types, or a structured input that recognizes different action fields. Understanding these differences will not only solve your immediate problem but also strengthen your overall GraphQL skills!

Happy coding!